This invention relates in general to the treatment of diseases of the spine using inter-vertebral devices and implantation methods. In particular, this invention relates to an automatically self-expanding inter-vertebral cage that can enter into a cavity through a small opening and automatically acquire any desired form as a result of being either released from an installation tool or from being exposed to environmental conditions, such as temperature, moisture, light, magnetic field, electric field, pressure, etc. (or the lack thereof). More particularly, the self-expanding inter-vertebral cage of this invention can utilize shape memory alloy materials to accomplish the automatic activation.
One of the most common causes for disability in people aged forty-five to sixty-five is pain in the lower back. Often, this is caused by compression of an inter-vertebral disc, which creates pressure on nerves extending from the spinal cord. Decompression spinal fusion procedures (also called inter-body fusion) are an effective means to reduce and, in some cases, eliminate numbness, weakness, and pain stemming from numerous medical conditions including, but not limited to, disc degeneration, spondylolisthesis, and disc herniation. There are also other causes of back pain, such as facet joint arthrosis, slipping of one vertebrae over another, deformity, and the like.
In cases of chronic back pain or weakness, spinal fusion procedures are usually recommended as a last resort. Procedures such as these share a relatively high risk of injury that coincides with the rewards of decompression of nerves and relief from debilitating pain. Thus, it is usually suggested that conservative management procedures, such as physical therapy, non-steroidal anti-inflammatory drugs, pain management, and muscle relaxing drugs be attempted and proven to unsuccessful in the treatment of the pain for at least six months before any surgical procedure is performed.
Although decompression spinal fusion procedures often succeed in removing the nerve pain, the pain related to instability between the two vertebrae often requires stabilization of the vertebrae level. Because the highest levels of stress and degradation of inter-vertebral bodies occurs in the lower (or “lumbar”) spine, this area is the focus of most fusion procedures, including posterior lumbar interbody fusion (PLIF), anterior lumbar interbody fusion (ALIF), transforaminal lumbar interbody fusion (TLIF), far lateral lumbar interbody fusion (FLLIF), and, more recently, extreme lateral interbody fusion (XLIF). The names of these surgical procedures denote the anatomical direction from which they are inserted. Each of these procedural approaches for implanting interbody fusion devices has its own set of advantages and disadvantages. As will be explained in greater detail below, this invention can be practiced using any of these techniques, as well as other techniques, in particular minimally invasive techniques.
A typical lumbar fusion device ranges in height from 10 mm to 20 mm based upon which motion segment is to be fused, as well as patient-specific measurements. The PLIF is one of the most flexible procedures, being able to access all lumbar and sacral motion segments. However, it is also one of the most dangerous procedures because of its close proximity to the spinal cord. Because of that, it has been determined that a minimally invasive device and procedure would be best suited for application in this surgical approach. The self-expanding inter-vertebral cage described and illustrated herein requires a much smaller incision compared to existing full-sized cages, which allows the cage to be elongated prior to insertion. As a result, the cage of this invention can be installed through a much smaller incision than previously available, an incision having a size that is approximately equal to a width of the elongated cage.